想把Serhii回答的Swift版本加进去。我用下面的代码创建了一个uibareextension .swift:

import Foundation
import UIKit

extension UINavigationBar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIToolbar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIView {
    fileprivate var hairlineImageView: UIImageView? {
        return hairlineImageView(in: self)
    }

    fileprivate func hairlineImageView(in view: UIView) -> UIImageView? {
        if let imageView = view as? UIImageView, imageView.bounds.height <= 1.0 {
            return imageView
        }

        for subview in view.subviews {
            if let imageView = self.hairlineImageView(in: subview) { return imageView }
        }

        return nil
    }
}

在子视图中找到发际线的一个很好的简短Swift函数是:

 func findHairLineInImageViewUnder(view view: UIView) -> UIImageView? {
    if let hairLineView = view as? UIImageView where hairLineView.bounds.size.height <= 1.0 {
        return hairLineView
    }

    if let hairLineView = view.subviews.flatMap({self.findHairLineInImageViewUnder(view: $0)}).first {
      return hairLineView
    }

    return nil
}

下面是破解方法。因为它在关键路径上工作，将来可能会崩溃。但就目前而言，它的运作符合预期。

迅速:

self.navigationController?.navigationBar.setValue(true, forKey: "hidesShadow")

Objective - C:

[self.navigationController.navigationBar setValue:@(YES) forKeyPath:@"hidesShadow"];

简单的解决方案

   let navigationBar = self.navigationController?.navigationBar
    navigationBar?.setBackgroundImage(UIImage(), forBarPosition: UIBarPosition.Any, barMetrics: UIBarMetrics.Default)
    navigationBar?.shadowImage = UIImage()

这里有另一个选择-我认为这只适用于你不需要半透明的导航栏(我没有)。我只是在导航栏的底部添加了一个1像素高的UIView(在导航栏下面1像素)，颜色与我的导航栏相同:

UIView *view = [[UIView alloc] init];
[view setBackgroundColor:self.navigationController.navigationBar.barTintColor];
[self.navigationController.navigationBar addSubview:view];
[view mas_makeConstraints:^(MASConstraintMaker *make) {
    make.height.equalTo(@(1.0f));
    make.leading.trailing.equalTo(self.navigationController.navigationBar);
    make.bottom.equalTo(self.navigationController.navigationBar).offset(1.0f);
}];

我正在使用砌体添加约束。

想把Serhii回答的Swift版本加进去。我用下面的代码创建了一个uibareextension .swift:

import Foundation
import UIKit

extension UINavigationBar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIToolbar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIView {
    fileprivate var hairlineImageView: UIImageView? {
        return hairlineImageView(in: self)
    }

    fileprivate func hairlineImageView(in view: UIView) -> UIImageView? {
        if let imageView = view as? UIImageView, imageView.bounds.height <= 1.0 {
            return imageView
        }

        for subview in view.subviews {
            if let imageView = self.hairlineImageView(in: subview) { return imageView }
        }

        return nil
    }
}